There are numerous circuits and other electronic devices that produce energy waves, such as electromagnetic waves and microwaves. These circuits produce energy waves that are delivered to a destination through different wires, guides, and other mediums.
Transitioning microwave signals from one mode to another or interfacing to another medium is “lossy.” The signal/energy is lost to radiation, metal losses, dielectric losses, and mismatch losses. By being lossy, a portion of the signal is lost as it travels through the circuits, wires, and other mediums. Stated another way, a signal entering a lossy material will be greater at the point of entry than at the point of exit.
Transitions at microwave frequencies are particularly difficult and lossy. Dielectric materials have higher loss tangents at microwave frequencies versus lower frequencies. At microwave frequencies metal losses become greater due to reduced skin depth and increased sensitivity to surface roughness. Apart from materials being lossier at microwave frequencies, the design of the transitions and interfaces is more difficult. It is difficult to control or predict phase at microwave frequencies. This leads to greater mismatch losses. Typically, the simpler an interface is, the less loss it will experience. One exemplary circuit that generates and transports microwaves is a “monolithic microwave integrated circuit” or “MMIC.” Lost signal waves are unusable and decrease the efficiency of a MMIC as the signal strength decreases due to loss. Generally, the higher the frequency of the microwave, the more lossy the transmission medium and more inefficient the circuit. In certain applications, even signal losses that reduce the signal small amounts, such as 1/10 of a decibel, may result in a significant performance loss. One exemplary application where loss from energy waves such as microwaves is problematic is a power amplifier.
One structure used to reduce lossiness is a waveguide. Waveguides are structures that guide energy waves with minimal signal loss. Unfortunately, signal loss is still problematic with certain waves because the connection or interface between the circuit generating the energy waves and the waveguide can be lossy itself. This is especially an obstacle with MMIC generated microwaves. Moreover, impedance miss-matches also cause signal losses. For example, the impedance of the MMIC, for example fifty ohms, may not match the impedance of the connected waveguide, which is much higher, typically several hundred ohms higher than the impendence of the MMIC. Moreover, the MMIC and waveguide also likely have a different modes of energy wave propagation. These types of interfaces are known generally as “impedance matching interfaces” or “impedance matching and transforming interfaces” and these interfaces transform impedance and wave mode propagation of the energy traveling through the interface. Throughout, the term “interface” is meant to denote an “impedance matching interface” or “impedance matching and transforming interface.”
Current interfaces between a MMIC and waveguide comprise numerous structures that include wirebonds, microstrips, pins, and other devices to connect a circuit to a waveguide or another structure. Each part of a matching network as associated loss. These interfaces also attempt to match and transform the impedance of the MMIC to the impedance at the waveguide. However, current impendence matching interfaces between an integrated circuit such as a MMIC and a waveguide still have an unacceptable amount of loss.
Current interfaces also use dielectrics to match impedance. While effective, interfaces that require dielectric materials are more expensive to produce and require a greater number or parts or materials as a dielectric must be included. Use of a dielectric also reduces the interface's efficiency as the dielectric also has an associated loss.
Therefore, it would be advantageous to provide an interface between an integrated circuit, such as a MMIC, and a waveguide, or other structure that reduces signal loss. It would also be advantageous to produce an interface that reduced loss that was inexpensive and easy to manufacture, particularly one that was constructed from parts that were commercially available and did not require the use of dielectric materials or microstrips.